Our work demonstrated that salivary gland extracts (SGE) from different species of blood-sucking leeches dramatically inhibit lung tumor colonization produced by intravenous injection of a variety of syngeneic murine tumors and the metastasis enhancement induced by local radiation and cancer chemotherapeutic drugs. To increase the potency of these effects and to determine their mechanisms of action, it is essential to isolate the antimetastatic principle(s) of SGE. Preliminary studies indicate that protein fractions of SGE can be separated with excellent resolution using alkaline polyacrylamide gel electrophoresis (APGE) and Fast Protein Liquid Chromatography (FPLC). After separation of SGE on APGE, protein bands were electrophoretically eluted and further purified on FPLC. All fractions were tested for antimetastatic activity and anticoagulant properties. We found that at least two protein species possessed both anticoagulant activity and high capacity to inhibit lung tumor colonization. These proteins were isolated in nearly homogeneous form having apparent molecular weights of 100,000 and 30,000. The proteins appear to inhibit either the activation or the actifity of factor Xa. Further experiments are in progress to investigate whether these proteins possess other properties that may be important in metastasis inhibition. (J)